This invention relates generally to vehicular vision systems and, more particularly, to a vehicular vision system which is operable to determine a distance from the vehicle to an object or light source remote from the vehicle. More particularly, the present invention is directed to determining the distance to an object whose image is captured by an image capture device. One application for the imaging system of the present invention is with a vehicle headlamp control and may identify particular light sources of interest and adjust a vehicle's headlamps according to the distance between the vehicle and the particular light sources.
Vehicle camera or vision systems have been proposed for various applications, such as rear and/or side view vision systems, back up aids, collision avoidance systems, rain sensor systems, head lamp control systems and the like. These systems may include a camera or sensor positioned on the vehicle for capturing an image of a scene exteriorly of the vehicle. The vision systems may also include a display for displaying a captured image, or may control an associated accessory on the vehicle, such as windshield wipers, headlamps or even the brake system in response to one or more characteristics of the captured image. In some applications, it has been recognized that distance information between the vehicle and an object in the captured scene may be helpful. In such applications, a ranging device may also be included to provide this information. Various ranging devices have been proposed, such as radar, ultrasonic, sonar, infrared beam/detector devices or similar proximity sensing devices. While such devices provide distance information to the associated vehicular system, this requires an additional sensing device separate from the vehicular vision or camera system, which adds to the bulk and costs associated with the system.
One vehicle system which distance information may be particularly useful is a vehicle headlamp control system for adjusting a vehicle headlamp in response to a detection of oncoming headlamps or leading taillights associated with other vehicles. To date, there have been many proposed headlight dimmer control systems. Many of the prior attempts at vehicle headlight dimming controls include a single light sensor which integrates light from a scene remote from the vehicle. The vehicle headlights are then dimmed when the integrated light exceeds a predetermined threshold. However, these systems typically require a sufficiently low threshold of detection such that many other lower intensity light sources may also be interpreted as headlights or taillights. These systems also have difficulties in reliably detecting taillights of other vehicles traveling ahead of the operative vehicle, since the intensity of taillights is typically substantially less than the intensity of oncoming headlights.
Other proposed headlight dimming controls implement an imaging array sensor which not only senses the light originating from both headlights and taillights, but may further determine the color and intensity of the light, thereby further determining whether the light source is a headlight or a taillight. Such systems are deficient in determining the distance between the sensed light source and the subject vehicle, which would be helpful modulating the headlamps in response to both the sensed light and the distance to the light. One proposed solution is to estimate the distance between the vehicle and the light source in response to the brightness or intensity of the sensed light source, since the detected signal from the light source may at times vary with the square of the distance to the light source. However, such a calculation is only accurate when the sensed light source intensity is within a predetermined level corresponding to a known or assumed intensity of headlamps and is at certain distances. Because the intensity of headlamps and taillamps vary between vehicles and may further vary as the headlamps are modulated between high and low beams and as the brake lights are activated or deactivated, such an estimation of distance may be inaccurate in many cases.